code: def pack_batch(batch):
      return batch["_single"]
  
file_path: fastNLP/fastNLP/core/collators/packer_unpacker.py
imports: from collections import defaultdict
  from functools import reduce
  from typing import Sequence, Mapping, Dict
label_desc: Use image node_id 2 for calling the SinglePackerUnpacker obj's underlying member method code with example usage: obj.pack_batch(batch) and returns: batch